AB1010 FACTORS ASSOCIATED WITH LONGITUDINAL BONE MINERAL DENSITY CHANGES IN RHEUMATOID ARTHRITIS
Authors: R. Ark, M. Bukhari
Journal: Annals of the Rheumatic Diseases (2022)

Background Rheumatoid Arthritis (RA) is a long-term inflammatory disorder affecting the joints. It is associated with osteoporosis, possibly linked to inflammation around affected joints and glucocorticoid medication. To our knowledge, longitudinal analysis of a UK based cohort of patients with RA has not been carried out. The impact of average tissue thickness on bone mineral density (BMD) has not been studied longitudinally in RA. Objectives This study aimed to identify factors that affect the rate of BMD change in patients with RA in a UK based cohort. Methods RA patients referred for multiple routine DEXA scans at the Royal Lancaster Infirmary from 2004-2019 were studied. Demographic and physical data such as age, sex, weight and height were collected. BMD in grams/centimetre2 and average tissue thickness were collected from DEXA images of the left and right hip (femoral neck and total femur), and the spine (L1-L4). BMD was modelled at the regions of the hip and spine using mixed-effects linear models. Age, sex, average tissue thickness and weight were used as explanatory variables. Results: Table 1 Effect size estimate (95% confidence interval) Location Sex Weight Average Tissue Thickness Left femur -0.104(-0.135,-0.074)* 0.004(0.004,0.005)* 0.022(0.018,0.025)* Left neck -0.088(-0.115,-0.061)* 0.003(0.002,0.003)* 0.015(0.012,0.019)* Right femur -0.136(-0.165,-0.106)* 0.004(0.004,0.005)* 0.022(0.018,0.026)* Right neck -0.06 (-0.094,-0.026)* 0.003(0.002,0.003)* 0.016(0.012,0.019)* L1 -0.001(-0.038,0.036) 0(-0.001,0.001) 0.003(-0.001,0.006) L2 0.007(-0.037,0.05) -0.001(-0.001,0) 0(-0.003,0.004) L3 0.021(-0.022,0.065) -0.001(-0.002,0) -0.001(-0.005,0.002) L4 0.01(-0.035,0.054) 0(-0.001,0.001) 0.001(-0.003,0.005) 1135 scans from 496 patients (80.4% female) with more than one scan were included, mean age was 64.1 (standard deviation 12.5). Fixed effect size and confidence intervals for each variable are shown in the Table 1. Female sex had a negative fixed effect at the hip but no significant effect on BMD change at the spine. Average tissue thickness had a significant positive fixed effect at all regions of the left and right hip, but no significant effect at the spine. Weight showed a significant positive fixed effect with BMD at the hip but no significant effect at the spine. Conclusion This study demonstrates that in RA patients, sex is associated with an increased rate of BMD loss at the hip but not at the spine. It also shows that weight and average tissue thickness are associated with lower BMD loss over time. This could be due to increased inflammation at the hip compared to the spine leading to osteoporosis. This study supports longitudinal data from other countries suggesting that factors associated with the rate of BMD change are different at the hip and the spine in RA (1). Average tissue thickness is associated with a reduced rate of BMD loss at the hip in RA patients, which is a novel finding. Average tissue thickness could be used in conjunction with other risk factors to help identify RA patients at risk of osteoporosis. This study may have been underpowered to detect changes at the spine. There may have been selection bias not all patients were routinely referred for repeat DEXA scans. References [1]Theander L, Willim M, Nilsson JÅ, Karlsson M, Åkesson KE, Jacobsson LT, et al. Changes in bone mineral density over 10 years in patients with early rheumatoid arthritis. RMD open. 2020; 6 (1): e001142. Disclosure of Interests None declared